
// There are 3 basic types in TypeScript
let isDone: boolean = false;
let lines: number = 42;
let name: string = "Anders";

// But you can omit the type annotation if the variables are derived
// from explicit literals
let isDone = false;
let lines = 42;
let name = "Anders";

// When it's impossible to know, there is the "Any" type
let notSure: any = 4;
notSure = "maybe a string instead";
notSure = false; // okay, definitely a boolean

// Use const keyword for constants
const numLivesForCat = 9;
numLivesForCat = 1; // Error

// For collections, there are typed arrays and generic arrays
let list: number[] = [1, 2, 3];
// Alternatively, using the generic array type
let list: Array<number> = [1, 2, 3];

// For enumerations:
enum Color { Red, Green, Blue };
let c: Color = Color.Green;
console.log(Color[c]); // "Green"

// Lastly, "void" is used in the special case of a function returning nothing
function bigHorribleAlert(): void {
  alert("I'm a little annoying box!");
}

// Functions are first class citizens, support the lambda "fat arrow" syntax and
// use type inference

// The following are equivalent, the same signature will be inferred by the
// compiler, and same JavaScript will be emitted
let f1 = function (i: number): number { return i * i; }
// Return type inferred
let f2 = function (i: number) { return i * i; }
// "Fat arrow" syntax
let f3 = (i: number): number => { return i * i; }
// "Fat arrow" syntax with return type inferred
let f4 = (i: number) => { return i * i; }
// "Fat arrow" syntax with return type inferred, braceless means no return
// keyword needed
let f5 = (i: number) => i * i;

// Interfaces are structural, anything that has the properties is compliant with
// the interface
interface Person {
  name: string;
  // Optional properties, marked with a "?"
  age?: number;
  // And of course functions
  move(): void;
}

// Object that implements the "Person" interface
// Can be treated as a Person since it has the name and move properties
let p: Person = { name: "Bobby", move: () => { } };
// Objects that have the optional property:
let validPerson: Person = { name: "Bobby", age: 42, move: () => { } };
// Is not a person because age is not a number
let invalidPerson: Person = { name: "Bobby", age: true };

// Interfaces can also describe a function type
interface SearchFunc {
  (source: string, subString: string): boolean;
}
// Only the parameters' types are important, names are not important.
let mySearch: SearchFunc;
mySearch = function (src: string, sub: string) {
  return src.search(sub) != -1;
}

// Classes - members are public by default
class Point {
  // Properties
  x: number;

  // Constructor - the public/private keywords in this context will generate
  // the boiler plate code for the property and the initialization in the
  // constructor.
  // In this example, "y" will be defined just like "x" is, but with less code
  // Default values are also supported

  constructor(x: number, public y: number = 0) {
    this.x = x;
  }

  // Functions
  dist(): number { return Math.sqrt(this.x * this.x + this.y * this.y); }

  // Static members
  static origin = new Point(0, 0);
}

// Classes can be explicitly marked as implementing an interface.
// Any missing properties will then cause an error at compile-time.
class PointPerson implements Person {
    name: string
    move() {}
}

let p1 = new Point(10, 20);
let p2 = new Point(25); //y will be 0

// Inheritance
class Point3D extends Point {
  constructor(x: number, y: number, public z: number = 0) {
    super(x, y); // Explicit call to the super class constructor is mandatory
  }

  // Overwrite
  dist(): number {
    let d = super.dist();
    return Math.sqrt(d * d + this.z * this.z);
  }
}

// Modules, "." can be used as separator for sub modules
module Geometry {
  export class Square {
    constructor(public sideLength: number = 0) {
    }
    area() {
      return Math.pow(this.sideLength, 2);
    }
  }
}

let s1 = new Geometry.Square(5);

// Local alias for referencing a module
import G = Geometry;

let s2 = new G.Square(10);

// Generics
// Classes
class Tuple<T1, T2> {
  constructor(public item1: T1, public item2: T2) {
  }
}

// Interfaces
interface Pair<T> {
  item1: T;
  item2: T;
}

// And functions
let pairToTuple = function <T>(p: Pair<T>) {
  return new Tuple(p.item1, p.item2);
};

let tuple = pairToTuple({ item1: "hello", item2: "world" });

// Including references to a definition file:
/// <reference path="jquery.d.ts" />

// Template Strings (strings that use backticks)
// String Interpolation with Template Strings
let name = 'Tyrone';
let greeting = `Hi ${name}, how are you?`
// Multiline Strings with Template Strings
let multiline = `This is an example
of a multiline string`;

// READONLY: New Feature in TypeScript 3.1
interface Person {
  readonly name: string;
  readonly age: number;
}

var p1: Person = { name: "Tyrone", age: 42 };
p1.age = 25; // Error, p1.age is read-only

var p2 = { name: "John", age: 60 };
var p3: Person = p2; // Ok, read-only alias for p2
p3.age = 35; // Error, p3.age is read-only
p2.age = 45; // Ok, but also changes p3.age because of aliasing

class Car {
  readonly make: string;
  readonly model: string;
  readonly year = 2018;

  constructor() {
    this.make = "Unknown Make"; // Assignment permitted in constructor
    this.model = "Unknown Model"; // Assignment permitted in constructor
  }
}

let numbers: Array<number> = [0, 1, 2, 3, 4];
let moreNumbers: ReadonlyArray<number> = numbers;
moreNumbers[5] = 5; // Error, elements are read-only
moreNumbers.push(5); // Error, no push method (because it mutates array)
moreNumbers.length = 3; // Error, length is read-only
numbers = moreNumbers; // Error, mutating methods are missing

// Tagged Union Types for modelling state that can be in one of many shapes
type State = 
  | { type: "loading" }
  | { type: "success", value: number }
  | { type: "error", message: string };

declare const state: State;
if (state.type === "success") {
  console.log(state.value);
} else if (state.type === "error") {
  console.error(state.message);
}

// Template Literal Types
// Use to create complex string types
type OrderSize = "regular" | "large";
type OrderItem = "Espresso" | "Cappuccino";
type Order = `A ${OrderSize} ${OrderItem}`;

let order1: Order = "A regular Cappuccino";
let order2: Order = "A large Espresso";
let order3: Order = "A small Espresso"; // Error

// Iterators and Generators

// for..of statement
// iterate over the list of values on the object being iterated
let arrayOfAnyType = [1, "string", false];
for (const val of arrayOfAnyType) {
    console.log(val); // 1, "string", false
}

let list = [4, 5, 6];
for (const i of list) {
   console.log(i); // 4, 5, 6
}

// for..in statement
// iterate over the list of keys on the object being iterated
for (const i in list) {
   console.log(i); // 0, 1, 2
}

// Type Assertion

let foo = {} // Creating foo as an empty object
foo.bar = 123 // Error: property 'bar' does not exist on `{}`
foo.baz = 'hello world' // Error: property 'baz' does not exist on `{}`

// Because the inferred type of foo is `{}` (an object with 0 properties), you 
// are not allowed to add bar and baz to it. However with type assertion,
// the following will pass:

interface Foo { 
  bar: number;
  baz: string;
}

let foo = {} as Foo; // Type assertion here
foo.bar = 123;
foo.baz = 'hello world'


